Microsize spherical polymer microparticles are utilized as cosmetic additives, supports for various chemical materials, spacers, column packings for chromatography, light diffusion agents, porosification agents, weight-lightening agents, antiblocking agents, surface modification agents for recording paper, etc.
In particular, hydrophilic crosslinked polymer microparticles can be utilized as hydrogel microparticles, and are useful as cosmetic additives, supports, porosification agents, weight-lightening agents, or surface modification agents for recording paper.
Producing polymer particles by suspension polymerization is conventionally widely carried out, and in particular producing hydrophilic crosslinked polymer particles by inverse phase suspension polymerization is also conventionally known. Conventional techniques for producing hydrophilic crosslinked polymer particles by inverse phase suspension polymerization employ a method in which a copolymer of an 8 or more carbons alkyl ester of acrylic acid and a (meth)acrylic compound having a polar group such as a carboxyl group is used as a dispersing agent (Patent Publications 1 and 2), a method in which a polyethylene oxide-based macromonomer is used (Patent Publication 3), a method in which a silicone compound is used (Patent Publication 4), etc.
However, in these conventional techniques, there are the problems that the dispersion stability of polymer particles during polymerization or after polymerization is not sufficient, the particle size of polymer particles obtained is nonuniform, and the hydrophilicity of polymer particles obtained is degraded. In particular, when hydrophilic crosslinked polymer particles with a high degree of crosslinking are produced by inverse phase suspension polymerization while increasing the proportion of a polyfunctional vinyl-based monomer used, polymerization stability is greatly degraded, and problems such as aggregation of particles, degradation in the quality of polymer particles obtained, and a reduction in productivity easily occur.    (Patent Publication 1) JP-A-1-213307 (JP-A denotes a Japanese unexamined patent application publication.)    (Patent Publication 2) JP-A-11-60616    (Patent Publication 3) JP-A-9-143210    (Patent Publication 4) JP-A-2003-34725    (Patent Publication 5) JP-A-2004-149569    (Patent Publication 6) International Patent Publication WO 01/04163    (Patent Publication 7) JP-A-2000-35697